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Biomedical subjects

T M Simon

Publications and source records attributed to T M Simon.

At least 19 recordsLinked to original sources
PubMed2006

Intra-articular distribution and residence time of Hylan A and B: a study in the goat knee.

OBJECTIVE: This study evaluates the viscosupplementation material Hylan A and B in relation to its: (1) joint distribution, residence time and mechanism of removal and/or degradation, and (2) associated synovial fluid leukocyte response, in a goat model. METHOD: One green fluorophore was covalently bound to the Hylan A low molecular weight (MW) molecule (viscous fluid fraction) and a second red fluorophore was covalently bound to Hylan B high MW molecule (globule gel-like fraction). Goats were anesthetized and the right knee received 0.5 ml of test material or unbound fluorophore dyes. Gross and histological serial evaluations were performed over an 8-week period. RESULTS: By 24 h, the non-covalently linked control labels were not present in the tissues. For the covalently linked labels, the green fluorophore Hylan A diminished rapidly in intensity grossly but persisted to 28 days within the superficial synovial and articular cartilage layers in histologic sections. The red fluorophore linked Hylan B was seen only as globules in the synovial fluid. Mononuclear cells remained attached to these globules for 28 days and showed phagocytosis of the globules as well as the green fluorophore Hylan A. The globules were absent at 56 days after injection. The synovial fluid leukocyte count peaked at 24h (mean 9767 cells/mm(3) +/- 8574 S.D.) and declined by 7 days. CONCLUSIONS: The smaller MW Hylan was removed more rapidly than the higher MW Hylan. The globules were degraded by a different mechanism involving monocytes/macrophages on the surface of the higher MW globules.

Animals↗
PubMed2001

Spontaneous repair of full-thickness defects of articular cartilage in a goat model. A preliminary study.

BACKGROUND: Full-thickness defects measuring 3 mm in diameter have been commonly used in studies of rabbits to evaluate new procedures designed to improve the quality of articular cartilage repair. These defects initially heal spontaneously. However, little information is available on the characteristics of repair of larger defects. The objective of the present study was to define the characteristics of repair of 6-mm full-thickness osteochondral defects in the adult Spanish goat. METHODS: Full-thickness osteochondral defects measuring 6 x 6 mm were created in the medial femoral condyle of the knee joint of adult female Spanish goats. The untreated defects were allowed to heal spontaneously. The knee joints were removed, and the defects were examined at ten time-intervals, ranging from time zero (immediately after creation of the defect) to one year postoperatively. The defects were examined grossly, microradiographically, histologically, and with magnetic resonance imaging and computed tomography. RESULTS: The 6-mm osteochondral defects did not heal. Moreover, heretofore undescribed progressive, deleterious changes occurred in the osseous walls of the defect and the articular cartilage surrounding the defect. These changes resulted in a progressive increase in the size of the defect, the formation of a large cavitary lesion, and the collapse of both the surrounding subchondral bone and the articular cartilage into the periphery of the defect. Resorption of the osseous walls of the defect was first noted by one week, and it was associated with extensive osteoclastic activity in the trabecular bone of the walls of the defect. Flattening and deformation of the articular cartilage at the edges of the defect was also observed at this time. By twelve weeks, bone resorption had transformed the surgically created defect into a larger cavitary lesion, and the articular cartilage and subchondral bone surrounding the defect had collapsed into the periphery of the defect. By twenty-six weeks, bone resorption had ceased and the osseous walls of the lesion had become sclerotic. The cavitary lesion did not become filled in with fibrocartilage. Instead, a cystic lesion was found in the center of most of the cavitary lesions. Only a thin layer of fibrocartilage was present on the sclerotic osseous walls of the defect. Specimens examined at one year postoperatively showed similar characteristics. CONCLUSIONS: Full-thickness osteochondral defects, measuring 6 mm in both diameter and depth, that are created in the medial femoral condyle of the knee joint of adult Spanish goats do not heal spontaneously. Instead, they undergo progressive changes resulting in resorption of the osseous walls of the defect, the formation of a large cavitary lesion, and the collapse of the surrounding articular cartilage and subchondral bone. CLINICAL RELEVANCE: As surgeons apply new reparative procedures to larger areas of full-thickness articular cartilage loss, we believe that it is important to consider the potential deleterious effects of a "zone of influence" secondary to the creation of a large defect in the subchondral bone. When biologic and synthetic matrices with or without cells or bioactive factors are placed into surgically created osseous defects, the osseous walls serve as shoulders to protect and stabilize the preliminary repair process. It is important to protect the repair process until biologic incorporation occurs and the chondrogenic switch turns the cells on to synthesize an articular-cartilage-like matrix. It takes a varying period of time to fill a large, surgically created bone defect underlying a chondral surface. The repair of such a defect requires bone synthesis and the reestablishment of a subchondral plate with a tidemark transition to the new overlying articular surface. The prevention of secondary changes in the surrounding bone and articular cartilage and the durability of the new reparative tissue making up the articulating surface are issues that must be addressed in future studies.

Animals↗
PubMed2001

Symptomatic articular cartilage degeneration: the impact in the new millennium.

The symptomatic degeneration of articular cartilage and associated arthritis is among the most prevalent chronic conditions in the United States and the population most at risk is increasing. It is the leading cause of limitations in activities of daily living and is second to heart disease in causing work disability. The current and future socioeconomic impact of chronic articular cartilage disease on the healthcare system will be magnified by increasing numbers of patients who will seek relief of their symptoms and their disability to remain active. Because these individuals live longer and remain active, the proportion of their life living with symptoms and disability from articular cartilage degeneration increases. The economic, psychologic, and social impact of degenerative articular cartilage can be enormous for these individuals but it also impacts their family and society. The direct traditional medical costs and indirect economic and wage loss from arthritis in individuals the United States has reached in excess of $65 billion annually and is expected to increase as the population ages. In addition, the expenditures for complementary and alternative professional services and therapies for arthritis is increasing and is also in the billions of dollars annually. Because of these escalating costs, documenting the value of the patient and cost effectiveness to society of prevention and treatment programs for symptomatic articular cartilage degeneration will be required.

Cartilage, Articular↗
PubMed1999

Reduced anterior tibial translation associated with adaptive changes in the anterior cruciate ligament-deficient joint: goat model.

Adaptive changes in the menisci and adjacent posterior capsule were documented within anterior cruciate ligament-deficient knee (stifle) joints in the goat model. These physical changes in the menisci and capsule developed over time and were associated with reduction in the initial (time zero) abnormal anterior tibial translation following transection of the anterior cruciate ligament. At 50 N of applied force, the normal goat knee joint has a total anterior-posterior translation of 0.6+/-0.1 mm (+/- SEM) at 45 degrees of flexion and 0.3+/-0.1 mm at 90 degrees. The translation immediately after transection (time zero) with 50 N of force was 8.2+/-0.5 mm at 45 degrees and 4.9+/-0.9 mm at 90 degrees. Within 8 months after transection and at 50 N of force, the treated knees had reduced translation values of 5.3+/-0.6 mm at 45 degrees of flexion and 2.9+/-0.5 mm at 90 degrees, or 35 (p<0.001) and 40% reductions, respectively, compared with the values at time zero. Magnetic resonance images of the ligament-deficient stifle joints, as well as gross measurements and image analysis after dissection, consistently demonstrated increases in cross-sectional area and volume of the menisci compared with the contralateral controls. These secondary changes were most pronounced in the posterior portion of the medial menisci, and histologic evaluation demonstrated hypercellularity with the accumulation of poorly organized collagen, reduced safranin O staining (proteoglycan matrix synthesis), a thickened capsule and capsule attachment, and increased vascularity at the meniscal capsule interface.

Adaptation, Physiological↗
PubMed1999

Tissue engineering principles in orthopaedic surgery.

Advances in the fields of biotechnology and biomaterials offer the orthopaedic surgeon the exciting possibility of repair or regeneration of tissue lost to injury, disease, or aging. The promising area of tissue engineering represents a multidisciplinary approach aimed at solving some of the most perplexing biologic problems, namely, the creation of new tissues and organs similar to the original tissues and organs. In addition, strategies using new synthetic polymer formulations can facilitate tissue replacement and represent alternatives to tissue regeneration in certain conditions. Although biotechnology has broad application over many medical specialties, orthopaedics is receiving a large focus of the research effort devoted to techniques for developing bone, articular cartilage, ligaments, and tendons. Because bioengineered tissue and/or techniques to stimulate tissue regeneration soon may be used clinically, orthopaedic surgeons should have a working knowledge of the basic concepts involved. Terms, such as biomaterial, biotechnology, matrices of synthetic or biologic polymers or both, adhesion, cohesion, porosity, induction, conduction, stem cell, progenitor cell, mesenchymal cell, tissue growth factor, bone morphogenetic protein, mitogenic and chemotactic factors, and numerous other terms will become part of the working language of clinicians of the twenty-first century.

Animals↗
PubMed1997

Characterization of the repair tissue after removal of the central one-third of the patellar ligament. An experimental study in a goat model.

UNLABELLED: The purpose of this study was to characterize the repair tissue that develops after removal of a portion of the patellar ligament for use as a graft. A six-millimeter-wide strip was obtained from the central portion of the patellar ligament with tibial and patellar bone plugs from one knee (stifle joint) of eight goats. The repair tissue that formed in the defect was characterized in terms of its structural, material, histological, and ultrastructural properties twenty-one months after the operation. The contralateral patellar ligament served as a control. Representative specimens were taken from the proximal, middle, and distal portions of the repair tissue and the control tissue for histological study and examination with transmission electron microscopy. The six-millimeter-long defect filled with repair tissue that increased the cross-sectional area by a mean of 42 per cent compared with the control values (p < 0.05). The maximum force to failure and the ultimate stress of the repair tissue were significantly decreased (by a mean of 51 and 65 per cent, respectively) compared with those of the controls (p < 0.001 for both). The stiffness also was reduced, by a mean of 27 per cent, but this was not significant (p > 0.05). Magnetic resonance imaging of the donor site showed slightly increased signal intensity compared with the intensity on the control side. Histological sections from the donor site contained collagenous (scar) tissue that was less organized, more cellular, and more vascular than the control tissue. Evaluation of the ultrastructure revealed that the repair tissue was composed primarily of collagen fibrils with a small diameter (range, fifty to 100 nanometers). CLINICAL RELEVANCE: The results of the present study suggest that the repair tissue that develops after removal of a strip of the patellar ligament for use as a graft is not comparable with normal tissue in terms of its structural, material, histological, and ultrastructural properties by twenty-one months. This should be kept in mind when this repair tissue is considered for use as a graft for revision of a reconstruction of the anterior cruciate ligament.

Animals↗
PubMed1996

Assessment of donor cell and matrix survival in fresh articular cartilage allografts in a goat model.

The long-term survival of allografts of articular cartilage has been proposed to be dependent on the survival of the cells that maintain the unique structural and material properties of the allograft. In this study, we assessed cell survival in 24 fresh articular cartilage allografts of the medial plateau in a Spanish-goat model. A DNA-probe technique was used to distinguish clearly between DNA from donor (allograft) and host cells. The intraarticular survival of viable allograft chondrocytes in the transplanted articular cartilage started to diminish as early as 3 weeks after transplantation; however, there was considerable variation in the amount of donor cell DNA detected in the allografts at 6 and 12 months following transplantation. This contrasts with our experience with fresh allografts of ligament, tendon, and meniscus, in which no donor DNA was detected 4 weeks after transplantation. DNA from host cells was present in all articular cartilage allografts, as evidenced by detectable unique host DNA patterns. Histological and histochemical assays showed that none of the transplants demonstrated normal structure and composition at 1 year after transplantation. The grafts in which large quantities of donor DNA were present appeared grossly superior to those with no or reduced remaining demonstrable donor DNA.

Animals↗
PubMed1996

Chondrocyte transplantation.

The transplantation of chondrocytes as a treatment to repair defects and degeneration in hyaline articular cartilage is being tested in numerous laboratory and clinical settings. This has included transplanting chondrocytes grown in tissue culture that were procured from non-weight-bearing areas of the affected joint to transplanting allografts with living chondrocytes in their intact cartilaginous matrix. Reported success with transplanting host and donor chondrocytes has varied and widespread application of these techniques still awaits more definitive studies. The clinician needs more evidence that the transplanted chondrocytes maintain their viability and that they synthesize the appropriate extracellular matrix. This new matrix needs to reproduce the functional, mechanical, and long-term wear properties of the native articular cartilage. Chondrocyte transplantation also merits further monitoring for possible delayed immunogenicity or for any signs of neoplastic potential. This exciting technology and its potential application to damaged and degenerated articular cartilage remains a stimulus to encourage further scientific work. Duplicating the unique and complex interrelations of the chondrocytes, matrix, and various bioactive factors is still some years away from general patient care.

Cartilage↗
PubMed1996

Biologic incorporation of allograft anterior cruciate ligament replacements.

Soft tissue allografts allow the orthopaedic surgeon to reconstruct ligaments without having to harvest additional tissue from the patient, which can eliminate donor tissue site morbidity and reduce surgical time. There is still much to be learned about the biologic aspects of the remodeling and incorporation of allografts in comparison with autografts. The interaction of cells, matrix, and biomolecules, such as growth factors, plays an important role that can potentially modulate, enhance, or impede the healing response in allografts. The authors have shown that, in the short term, allografts used in anterior cruciate ligament reconstruction are not as rapidly remodeled and incorporated into host tissue as are autografts. The long-term implications of this slower allograft incorporation in anterior cruciate ligament reconstruction are still unknown. The cells that repopulate allografts and autografts favor production of smaller diameter collagen fibrils, which in sufficient numbers can provide significant strength. Use of allografts raises other issues and potential disadvantages, including scarcity, immunogenicity, the potential for disease transmission, and cost-effectiveness in anterior cruciate ligament reconstruction.

Animals↗
PubMed1995

Preparation of an exogenous fibrin clot.

Exogenous fibrin clot has been proposed to promote the healing of meniscal tears in areas of compromised vascularity. We present a method to reproducibly prepare a tightly wound exogenous fibrin clot using 5 to 10 mL of blood obtained by sterile venipuncture. The technique produces a clot of increased consistency and high fibrin content that is adaptable in preparation as a longer, thinner clot or a shorter, thicker clot. Clots prepared in this manner will hold suture or can be morselized for extrusion through a syringe.

Animals↗
PubMed1995

Assessment of initial fixation of endoscopic interference femoral screws with divergent and parallel placement.

Divergence of the interference screw placement used for femoral fixation during endoscopically assisted reconstruction of the anterior cruciate ligament has been described. This study is a biomechanical evaluation in 12 pairs of fresh intact bovine knees of femoral interference screws placed divergently and parallel relative to the bone block and its tunnel. One knee of each pair had the interference screw placed in a parallel fashion and the other knee had a 15 degrees divergence from the bone plug. Paired specimens were used to provide an optimal comparison of biomechanical data of the two different screw placements. No statistically significant differences were seen between the two groups when looking at ultimate load, deformation, and stiffness. Mode of failure was of more concern: in 4 of 12 divergent constructs, bone plug pullout occurred compared with only 1 of 12 in the parallel construct. The pullout strength remains high even with divergence of up to 15 degrees between the bone plug and femoral interference screws placed endoscopically.

Animals↗
PubMed1995

Comparison of pullout strength for seven- and nine-millimeter diameter interference screw size as used in anterior cruciate ligament reconstruction.

This study compares biomechanical properties of 7- and 9-mm diameter screws providing interference fixation in anterior cruciate ligament reconstruction. Sixteen pairs of fresh-frozen bovine knees were evaluated. Uniaxial load to failure was performed at a deformation rate of 30 mm/s along the mechanical axis of the ligament graft with the knees secured at 45 degrees of flexion in a custom jig. A video analyzer was used to measure ligament strain and bone-to-bone deformation. Ultimate force, deformation, and failure mode were recorded and compared. The 7-mm screws provided 98% yield strength, and 95% ultimate force compared with the 9-mm screws. The average femoral pullout strength was 1161 +/- 93 N in the 7-mm group and 1198 +/- 142 N in the 9-mm group. Failure mode was similar in both groups. Clinically, the usage of 7-mm screws may reduce iatrogenic injuries to the patellar tendon graft compared with larger screws. This study shows that the biomechanical advantages of 9-mm screws compared with 7-mm screws are minimal.

Animals↗
PubMed1993

Arthroscopic assisted PCL reconstruction: a technical note on potential neurovascular injury related to drill bit configuration.

Neurovascular injury is a potential complication during arthroscopic assisted or open posterior cruciate ligament (PCL) reconstruction. The anatomical configuration of the posterior tibia and the square configuration of the end of commonly used drill bits require special attention. One portion of the drill bit may cut out of the tibia < or = 20 mm distal to the exit point of the guide wire. The sharp square edges of these drill bits have a greater potential to traumatize adjacent soft tissue and to increase the risk of neurovascular damage. This risk may be decreased by using a tapered drill bit, an oscillating drill, and careful elevation and retraction of the overlying soft tissue.

Adult↗
PubMed1993

Endoscopic ACL reconstruction: a technical note on tunnel length for interference fixation.

The total length of bone-patella tendon-bone autografts can vary significantly between individuals. Grafts that are "too long" may protrude from the tibial tunnel site, precluding interference screw fixation. A simple calculation can be used to estimate the length of the tibial tunnel required to accommodate the graft. An intraoperative final check can be made with a calibrated drill. This distance should accommodate the total graft length. If necessary, minor adjustments that include trimming the bone plugs or deepening the femoral osseous tunnel can be made to prevent graft protrusion.

Anterior Cruciate Ligament↗
PubMed1993

Endoscopic ACL reconstruction.

The endoscopic technique offers the advantage of one incision and a femoral osseous tunnel trajectory that is more in line with the collagen fibers of the graft. Technically, it is more demanding to reproducibly obtain the interference fixation than using the two-incision technique. There is a tendency for screw and graft divergence in the femoral tunnel. The exact clinical significance of this screw and bone plug divergence has yet to be clarified. Surgeons must assess their ability to obtain the best results for the patient. There is a definite learning curve for the endoscopic technique. We believe that, with further advances in instrumentation, fixation, and alternative grafts, it will eventually be the approach of preference for ACL reconstructions.

Anterior Cruciate Ligament↗
PubMed1992

Survival of cells after intra-articular transplantation of fresh allografts of the patellar and anterior cruciate ligaments. DNA-probe analysis in a goat model.

The fate of donor cells in fresh allografts of the patellar and anterior cruciate ligaments was assessed after transplantation of the allografts as substitutes for the anterior cruciate ligament in goats. DNA-probe analysis was used to distinguish between the DNA of individual goats. Donor DNA was completely replaced by recipient DNA in both the transplanted patellar and anterior cruciate ligaments within a four-week period. Simultaneous full-thickness skin transplants in the same animals were not rejected during the interval of rapid loss of donor DNA from the allografts. The absence of rejection of the skin grafts at the one-week interval suggests that no pre-existing antibody associated with an immune reaction was responsible for the rapid loss of DNA in the allografts.

Animals↗
PubMed1991

The effects of in situ freezing on the anterior cruciate ligament. An experimental study in goats.

We developed an in situ freeze-thaw model designed to simulate an ideally placed and oriented autogenous graft of the anterior cruciate ligament. In this model, the anterior cruciate ligament was exposed, and the femoral insertion, tibial insertion, and body of the anterior cruciate ligament were frozen in situ with specially designed freezing probes. Freeze-thaw cycles were repeated five times. We used the technique in thirty-three mature goats to study the biological and biomechanical outcomes of the devitalized and devascularized anterior cruciate ligament at zero, six, and twenty-six weeks after treatment. Thus, the collagen fibers of the simulated autogenous graft remain in normal anatomical position and the simulated graft is fixed under physiological tension. At twenty-six weeks, no statistically significant differences were noted between treated and contralateral control (untreated) ligaments relative to anterior-posterior translation, maximum force to rupture, stiffness in the linear region of the force-length curve, modulus of elasticity in the linear region, strain to maximum stress, or maximum stress. The only statistically significant difference was an increase in cross-sectional area of the ligament. This increase was 22 and 42 per cent greater than that in the control ligaments at six weeks and six months. At six months, the ligaments in the control group had an average mid-cross-sectional area of 17.7 +/- 1.2 square millimeters and the ligaments in the experimental group, 25.2 +/- 3.1 square millimeters. Changes in the size and density of the collagen fibrils also were demonstrated at six months. These observations are in sharp contrast to our previous studies of replacement of the anterior cruciate ligament, in which an allograft of the ligament or an allograft supplemented with a 3M ligament augmentation device (LAD; 3M, St. Paul, Minnesota) was used. In those studies, an average reduction in maximum strength of 75 per cent for the allografts and 50 per cent for the allografts that had a ligament-augmentation device was found at one year. We concluded that devitalized, devascularized anterior cruciate ligaments do not lose strength if the anatomical position and the orientation of the collagen fibers are not altered.

Animals↗